1) Field of the Invention
The present invention relates to a chuck device which holds a tool such as a drill or a workpiece to be processed in a machine tool.
2) Description of the Prior Art
In a chuck device of the prior art, a number of rollers are arranged in a wide range between a tightening cylinder and a rotary cylinder fitted to the tightening cylinder to install a substance to be held, such as a tool or a workpiece. The rollers do not intersect the axial line of these cylinders but make a suitable tilt angle with respect to the axial line. The rotary cylinder is rotated and each roller revolves on its axis and round the axial line in spiral form. The tightening cylinder is contracted and the substance to be held is tightened and held by the inner circumferential surface of the tightening cylinder. Because a large force is required to contract the tightening cylinder, a large force is also required to rotate the rotary cylinder.
In order to solve the problem in the prior art, a plurality of grooves in parallel to the axial line of the tightening cylinder are provided on the inner circumferential surface of the tightening cylinder.
In this construction, since the inner circumferential surface of the tightening cylinder is separated in the circumferential direction, stability of the substance to be held is deteriorated when the substance is held.